1. Field of the Invention
The invention relates to a longitudinally controllable adjustment device, including a cylindrical housing closed at one end and filled with a pressure medium, a piston rod sealingly extending from the other end of the housing and slidable therein. A piston is disposed in the housing and sealingly guided against the inner wall thereof, which is fixedly connected with the piston rod and slidable together with it and which divides the inner chamber of the housing into two partial chambers. A valve connects or separates the two partial chambers, having a valve body actuable by means of a slidably guided trigger pin and which abuts with one sealing face against a seal and can be slidingly brought into a position bridging the seal by means of a tapering section.
2. The Prior Art
There are two basic groups of such adjustment devices. The one group is known, for example, from German Utility Models DE-GM 74 34 098, DE-GM 74 34 102, DE-GM 74 34 101 and DE-GM 86 01 132 (corresponding to Published, Non-Examined European Patent Application EP-OS 0 234 184). In this group of adjustment devices the valve is disposed in the piston. In the other group of adjustment devices, as for example known from U.S. Pat. No. 3,656,593, the valve is disposed in that end of the housing which is opposite the side where the piston rod exits. Both types of adjustment devices are at least partially filled with gas, by means of which the piston rod can be pushed out of the housing or it can be pushed back in against the force of its pressure, when the valve is opened. If the piston itself is slidable in a fluid-filled chamber, then a complete, i.e., for all practical purposes rigid, arrestment of this adjustment device, which can also be called a gas spring, becomes possible. If, however, the entire housing is filled with pressure gas, a spring potential having a very steep distance/force line is possible, even with the valve closed. Depending on the design, the valve can be either a so-called short-stroke valve or a so-called long-stroke valve. With a so-called short-stroke valve the trigger pin needs to be moved in its longitudinal direction only by a very short distance, for example, from a few tenths of a millimeter up to 1 or 2 mm, while with a long-stroke valve the trigger pin must be moved by at least several millimeters, for example 3 to 6 mm, before the valve opens. For these purposes the valves must be basically differently designed and manufactured.